1. Field of Invention
The present invention relates to a method for producing ammonium hexachlororuthenate by way of precipitation from a hydrochloric acid solution containing ruthenium, a method for producing ruthenium powder, as well as ammonium hexachlororuthenate.
2. Description of Related Art
Ruthenium powder can be produced by adding ammonium chloride to a hydrochloric acid solution containing ruthenium, heating the solution so as to form ammonium hexachlororuthenate (NH4)3[RuCl6], precipitating and filtering it, and baking the precipitated crystals in reducing atmosphere.
Patent Document 1 (Japanese Unexamined Patent Publication (kokai) No. 2007-230802) proposes a method for producing crystals of precipitated ruthenium. According to the disclosed condition for forming ammonium hexachlororuthenate, a hydrochloric acid solution containing ruthenium is held at from 80 to 95° C. for 3 hours or longer, ammonium chloride is added to the solution held as mentioned above, and the temperature of from 80 to 95° C. is maintained for 1 hour or longer. The moisture content of the precipitated crystals of ammonium hexachlororuthenate is 16.1% or more according to the examples of Patent Document 1.
Since the ruthenium obtained by baking the ammonium hexachlororuthenate is hard sintered product, pulverization thereof is not easy. The ruthenium powder is liable to be contaminated by worn parts of a pulverizing mill. Patent Document 2 (Japanese Patent No. 3990417) proposes a method for producing a ruthenium powder which is easy to pulverize. According to the proposed method, ammonium hexachlororuthenate (NH4)3[RuCl6] is baked at 500 to 800° C. to produce crude ruthenium powder. This is pulverized and then re-baked at 800 to 1000° C. The proposed two-stage baking method enables to obtain a sintered product which is less hard.